Masashi Koyanagawa

Study on Thermal Stresses in Continuously Reinforced Concrete Pavement

In the structural design of continuously reinforced concrete pavement (CRCP), thermal stresses should be properly taken into account. Thermal strains and temperatures in concrete slabs were measured on test sections of CRCP. Measured strains were divided into axial, curling, and nonlinear components, and each component was examined. It was found that the curling component is predominant in terms of transverse stress, which is important in the structural design. However, the maximum thermal stress is reduced by 25 percent because of the nonlinear component. On the basis of the results, a procedure for estimating the thermal stress in CRCP was proposed.

TEMPERATURE GRADIENT OF CONCRETE PAVEMENT SLAB OVERLAID WITH ASPHALT SURFACE COURSE

In the structural design of composite pavement with a concrete pavement slab overlaid with an asphalt surface course, it is very important to estimate the temperature gradient in the concrete slab. An asphalt surface course reduces the temperature gradient in an underlaid concrete slab, resulting in the reduction of thermal stress of the concrete slab. This effect was investigated by temperature measurement in model pavements and by thermal conductivity analysis. Thermal properties were estimated by a backanalysis by using measured temperatures over 1 year. From the numerical simulations varying the thickness of asphalt surface and concrete slab, the relationship between the reduction effect and the asphalt thickness was derived as a function of the thickness of asphalt surface course, which can be used in the structural design of the composite pavement.

Thermal Stress Calculation Method for Concrete Pavement Based on Temperature Prediction and Finite Element Method Analysis

A method to predict thermal stress of a concrete slab was developed in this study. In this method, temperatures and thermal stresses in a concrete slab are predicted by solving a one-dimensional heat transfer equation with the control volume method and three-dimensional finite element method (3DFEM). Predicted temperatures were compared with those measured in various regions in Japan to validate the method. The thermal strains calculated with 3DFEM were also compared with those measured in test concrete pavement slabs to confirm the method’s validity. The relative frequencies of thermal stress for one year were obtained from the calculated stresses. In thin slabs (20 and 23 cm), tensile thermal stress at the bottom was greater than those estimated with the current thermal stress equation, which considers internal stress due to the nonlinearity of the temperature profile in the slab. In thick slabs (25 and 30 cm), by contrast, the current thermal stress equation gave almost the same thermal stress as the finite element method did, although the peak time for the maximum tensile stress was delayed in the thick slabs. The proposed method can be applied to a variety of concrete pavement structures under various temperature conditions.

TWO LAYERD BASE COURSE THICKNESS DESIGN METHOD OF CONCRETE PAVEMENT USING RELIABILITY BASED DESIGN CURVES

In the past study that a research group of Tokyo University of Agriculture, Ishikawa National College of Technology, Public Works Research Institute and Japan Cement Association carried out, design curves of the crusher-run base, the mechanical stabilized base and the cement treated base considering reliability were proposed based on bearing capacity research results of an actual size concrete pavement / base course yard constructed in the Public Works Research Institute and the past researches. However the two layered base course design method was not examined. Consequently in this study, change of bearing capacity of the two layered base course surface was examined using the Monte-Carlo simulation when the reliability level of design curves were changed, and as a result a simple reliability calculation method was proposed. 東京農業大学，石川工業高等専門学校，(独)土木研究所および(社)セメント協会の研究グループでは，土木研究所内に施工した実大コンクリート舗装および実大路盤試験区での路盤支持力測定試験結果および既往の支持力測定結果を統計分析し，信頼性分析結果に基づいて信頼度に応じたクラッシャラン，粒度調整砕石，セメント安定処理路盤の路盤厚設計曲線を提案した．しかい，2層系路盤を構築する場合についての検討は行っていない．そこで本研究では，モンテカルロシミュレーションによって信頼度が異なる路盤厚設計曲線を用いた場合の2層系路盤上での支持力がどの程度になるかを検討し，簡易な信頼度算出方法を提案した．

MIX PROPORTION OF PAVEMENT CONCRETE USING VARIOUS AGGREGATES

Wide use of concrete pavement is expected as its excellent durability and reduced life cycle cost. For further use of concrete pavement, introduction of performance based design concept instead of descriptive specification for constituent materials and consistency for concrete is necessary. Usage of limestone for coarse aggregate of general ready mixed concrete is increasing to reduce drying shrinkage, however application of the limestone aggregate to concrete for pavement is questionable for its performance of skid resistance and abrasion. On the other hand, effective use of slag aggregate are required from the environmental aspect. Therefore, it is studied with the purpose to clarify the applicability to the pavement concrete of various coarse aggregates. Physical properties test of various coarse aggregate and trial mixing of concrete using the aggregates were conducted. As a result, the unit content of water and bulk volume of coarse aggregate per unit volume concrete of a river gravel, a crushed stone, and limestone aggregate was almost usually a passage. However, unit content of water increased slag aggregate a little. コンクリート舗装は，耐久性が高くライフサイクルコストが低減できるため，普及が期待されている．コンクリートの主要材料である粗骨材は，天然砂利が減少し，砕石や石灰石骨材が増えている．また，産業廃棄物削減を目的に各種スラグ骨材の有効利用が求められるなど，骨材資源が多様化している．そこで，各種粗骨材の舗装コンクリートへの適用性を明らかにすることを目的に研究を行なっている．本報告では，各種粗骨材の物性試験と，それらの粗骨材を用いてコンクリートの配合試験および強度試験を行なった結果について取りまとめた．使用した粗骨材のすりへり減量は，13～33％の範囲であった．配合試験の結果，砂利，砕石，石灰石骨材の単位水量，単位粗骨材かさ容積はほぼ通常どおりであったが，スラグ骨材は単位水量がやや増加した．

RELIABILITY OF BASE-COURSE THICKNESS DESIGN CURVES FOR CONCRETE PAVEMENTS IN JAPAN

本研究では，（独）土木研究所の舗装走行実験場に施工した実大コンクリート舗装試験区，実大路盤試験区での路床，路盤の支持力調査結果および既往の研究事例に基づき，路盤厚設計曲線の信頼性に関する検討を行った．その結果，クラッシャラン，粒度調整砕石の設計曲線の信頼度はそれぞれ80％，70％であること，セメント安定処理路盤の設計曲線は路盤厚によって信頼度が異なっていることがわかった．また，これらの結果に基づき，本研究では信頼度に応じた各路盤材料の設計曲線を提案した．

TEMPERATURE GRADIENT OF CONCRETE PAVEMENT SLAB OVERLAID BY ASPHALT LAYER

コンクリート舗装版を基層とし, アスファルトを表層に持つコンポジット舗装の設計においては, コンクリート舗装版内の温度勾配の算定が非常に重要である. アスファルト表層の存在によってコンクリート版内の温度勾配が低減され, それにともなって温度応力が減少するからである. 本研究においては, このような温度勾配の低減効果を, モデル舗装における温度の実測, その実測データを用いた逆解析, さらに熱伝導解析によって検討した. これらの結果に基づいて, アスファルト表層厚と温度勾配低減効果の関係を求め, その関係を温度勾配低減係数という構造設計に適用可能な形で提示した.

A STUDY ON THE INFLUENCE OF THE TEMPERATURE DIFFERENCES WITHIN THE CONCRETE SLABS ON THE RESULTS OF FWD TEST

Concrete Slabs are warped by the temperature differences within slabs, and there are possibility that the contact between slabs and base course is lost. The deflection mesurements by the FWD test operated under such conditions are influenced by the contact condition. Consequently, the backcaluculation moduli of the same concrete pavement differs according to the time of test. In this paper, from the results of the FWD test on the controlled test pavement operated continuously in the period of 24 hours, the relationship among the slab temperature difference, the deflection measurement, the effect of load transfer, backcalculated k-value were investigationed. As the results, the backcalculated k-value were able to correct accorging to the slab temperature gradient.